Hitachi RAI-50NH5 - Page 74

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● R500, R253, detect the DC voltage at the power circuit. The microcomputer receives a DC voltage (260-
380V) via HIC
37 and applies correction to the overload set value so the DC current is low (high) when
the DC voltage is high (low).
(Since the load level is indicated by the DC voltage multiplied by DC current, R247, R248, R249 are
provided to perform the same overload judgement even when the voltage varies.)
< During start current control >
● It is required to maintain the start current (DC current) constant to smooth the start of the DC motor for
the compressor.
● RAC-50NH5 uses software to control the start current.
● The start current varies when the supply voltage varies. This control method copes with variations in the
voltages as follows.
(1) Turns on the power module's U
+
and V
–
transistors so the current flows to the motor windings as
shown in Fig8-9.
(2) Varies the turn-ON time of the W
+
transistor according to the DC voltage level and the start is
controlled so the start current is approx. 10A as shown in Fig. 8-10.
Fig. 8-8
DC current
G
0
0
Rotation speed
Amplification : low
DC voltage : low
DC current : high
Amplification : high
DC voltage : high
DC current : low
Amplification : 8.5 times
DC voltage : 260V
U
+
U
—
V
+
V
—
W
+
W
—
U
V
W
Compressor motor
DC current
Power module
DC 260-360V
Detection
resistor
Fig. 8-9
Fig. 8-10
20
15
10
5
0
DC current (A)
W transistor
ON-time
Start
DC voltage (start current)
Set value
Time
Chopper duty: high
DC voltage: low
DC voltage: 280V
DC voltage: high
0274E Pg 57-88(RAI-50NH5) 19/10/05, 3:35 PM84